The present invention generally relates to apparatus and methods for providing vapor barriers and, more specifically, to apparatus and methods of inhibiting the migration of harmful vapors from the ground.
Many parcels of land are contaminated with harmful substances. Some sites may be contaminated by naturally occurring substances, such as Radon, or Methane. More commonly, sites are contaminated by industrial or commercial uses. For example, land and groundwater often becomes contaminated by factories, chemical processing plants, dry cleaning facilities, gasoline service stations, landfills and other facilities. When such parcels of land are no longer needed for these operations, they may sit idle because of the high cost of removing the contaminants.
In some cases, land has been contaminated by such high levels of hazardous waste or pollution that it is considered un-developable. Such sites are sometimes designated as hazardous waste sites or Superfund sites. In other cases, the level of contamination, and the cost to restore the land, may be low enough that the land is a candidate for redevelopment. In the U.S., such sites are often referred to as “Brownfields”. There has been an increase in the number of developments on Brownfields partly because these sites often exist in high-population density areas where there is a great demand for developable land.
Because of these trends, there has been an increased demand for economical ways to make Brownfields suitable for redevelopment. In some cases the contaminants may be removed. In many cases, however, it is either not possible, or practical, to remove all of the contaminants. In these cases, development may still be possible if ways are found to protect future occupants of the site from exposure to the hazardous substances at the site. One way to do this is to incorporate a barrier beneath newly constructed buildings that will inhibit the upward migration of chemical contaminants into the construction materials and indoor air space of the structure.
Unfortunately, past techniques for providing effective barriers to hazardous substances to make land safe for redevelopment have had a number of drawbacks, including high cost and difficulties in installation, or they may have not provided an adequate level of isolation from contaminant vapors. For example, various forms of polyolefin sheeting have been used as barriers to contaminant vapor intrusion. These may comprise low and medium density polyethylene, which is laid down in an overlapping pattern. The overlaps are then chemically sealed or heat welded to produce a continuous sheet. Penetrations through the membrane (e.g. sewer piping, electrical conduit, etc.) are sealed by wrapping and mechanically binding the membrane to the penetrating object. The use of these membrane materials for vapor barrier application is very labor intensive as the seam binding/welding and mechanical sealing of penetrations requires significant time by skilled technicians to ensure membrane integrity.
Latex modified asphalt sprays have also been used as a low cost alternative vapor barrier. Typically, the material is spayed onto the ground surface. In some cases, the asphalt may be applied over a typical geo-textile fabric, which serves to add tensile strength, but is not a barrier to vapor movement. During application, when encountering a penetration (e.g. conduit protruding upward) sealing around the protrusion is easily accomplished by spraying the asphalt-based material from the ground surface up to and contacting the protrusion, thus making a continuous seal. Asphalt-based membranes have been shown to perform well as barriers to water, but have limited ability to inhibit volatile organic vapors (e.g. gasoline, degreasing solvents, etc.) commonly found on previously polluted properties. In fact these membranes will be degraded by many of the chemicals commonly found on polluted sites (benzene, perchloroethene, etc.).
As can be seen, there is a need for improved ways to provide a barrier to hazardous materials that protects occupants of contaminated land, in a way that is effective, economical and easy to install. There is also a need for a contaminant vapor barrier that is easy to install on buildings which have penetrations through the barrier surface. There is also a need for a contaminant vapor barrier that is not degraded by the chemicals present on polluted sites.